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Regulated Luminosity Lamp

Constant Brightness til end of life
  [vote for,

[Footnotes at the bottom, to avoid clutter]

All modern lighting technologies[1] will gradually decrease in brightness over the course of their lifespans... the longest lived lights, at the end of their rated lifespan, are 30% less bright than they were when brand new[2].

Lighting manufacturers will tell us that this depreciation isn't a problem for a variety of reasons[3], but in reality, it is indeed a problem, for a variety of other reasons[4].

This idea is to design a lamp which has an electronic light sensor (located so that it can "see" some of the light produced by the lighting element) in it's circuit, and a microcontroller to regulate the amount of power sent to the lighting element, such that the lamp's brightness remains constant until such time that the lighting element cannot efficiently produce the targeted number of lumens, after which it would shut down.

Obviously, this means that the lamp's brightness at the beginning of it's life is rather less than what the brand new lighting element could potentially produce, but the constancy of brightness, and the extend lifespan, make up for it.

[1] This applies to all of: Incandescent lamps (including tungsten and halogens), fluorescent and other arc lamps (including linear fluorescents, circlines, CFLs, and induction lamps), LED lamps, Electroluminescent wire, EL tape, and Electron Stimulated Luminescent lamps. There are probably others which I'm not aware of, but I think I've got most of the bases covered.

[2] If a lamp is so old that it's maximum brightness is 70% of what it was when it was new, then it has, /by definition/ reached the end of it's lifespan, even if it is still functioning. Many long-lived lamps continue to function, and continue to grow ever dimmer, even beyond their proper lifespan. I call such bulbs, which are overdue for replacement, zombie bulbs :).

[3, 4] Supposedly, because the loss of brightness is gradual, a human won't notice that an old lighting element produces less light than when it was new...

This is true, only if the lamp is in isolation. If I have a light fixture with several lamps, or a ceiling with several recessed fixtures, and I replace one, I will probably notice that the other, similarly old lamps, are dimmer than the new one... potentially leading me to replace the old lamps, even if they had a few good years left in them.

Futhermore, if a person /doesn't/ realize that a lamp has dimmed over it's life, then when it burns out and he has to replace it, he will believe (falsely) that it had been just as bright when it had been new... and since it was quite dim when it burnt out, it must have been quite dim when it was new! This would lead that person to replace the burnt out lamp with a higher wattage one, resulting in too much light, and too much energy use. This is especially true of zombie bulbs[2].

Lastly, lighting manufacturers tell us that if a lamp gave ample light when it was new, it will be just sufficient when it reaches the end of it's life. The problem is that many people purchase lights which produce just barely enough light when new, and which become insufficient, before the end of their lifespans. In such a case, the bulb's practical lifespan is less than it's rated lifespan, because as soon as the consumer tosses it in the garbage, it's effectively dead.

PS: I happen to work in retail, and one of the things the store I work in sells is light bulbs. Many people refuse to by CFLs because, supposedly, "They're too dim." This reason isn't the least bit logical, since one can always choose to purchase the higher wattage CFL. The only reason I can think that any person would make such a complaint is that they don't realize that CFLs dim with age.

PPS: It might make sense for some exceptionally long- lived lamps to have a manual switch which selects from two different luminosities. When the lighting element is too old to produce the highest luminosity, the user removes it from the fixture, sets the switch to a lower setting, then installs it in a different light fixture, where the lower light level is correct for that fixture. Does anyone know a non-evil sounding term for an undead light bulb?

goldbb, Jun 14 2012

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       If done correctly, this will also increase the life span of the lamp, because it will be driven at less than it's capacity for much of it's life.   

       We're actually building exactly this feature into an LED unit for work, although it's a bit higher intensity than your average household bulb (also a bit pricer, somewhere around $10k/unit).
MechE, Jun 14 2012

       My computer monitor here is an LCD type with CFLs in it (like most of them; the LED-lit displays are still fairly new). I always set the "brightness level" to ZERO. CFLs can't actually do zero brightness and still be on; they simply have some minimum output level.   

       The room in which this monitor is located has dim lighting. The monitor is, in comparison, quite bright enough. And I'm hoping it will last a nice long long time.
Vernon, Jun 14 2012

       Bigsleep -- and that is why light bulbs made for sale in America must now, by law, be packaged with the number of lumens displayed very prominently.   

       MechE -- cool! Although $10k is a lot for a light fixture. Are gold ingots involved?
goldbb, Jul 18 2012

       possible solution: most houses in North America are 2 phase, so if the bulb can handle it at all, just flip over to 230V (instead of 115) and it will be brighter.
FlyingToaster, Jul 18 2012

       I can't help thinking that the end of this idea could have been brought substantially closer to the beginning. Nevertheless, [+].
MaxwellBuchanan, Jul 18 2012

       //packaged with the number of lumens displayed very prominently//   

       I don't know if it's law or not, but when I went to buy a bulb yesterday, they were all labelled prominently with the lumen output.
MaxwellBuchanan, Jul 19 2012

       goldbb- Well the boards are gold plated, but the main cost driver is the optics and controls.   

       FT- For LEDs doubling the voltage wouldn't do anything but fry the control electronics. LED brightness is controlled by regulating current at a fixed voltage.
MechE, Jul 19 2012

       Even lumens are a bit problematic; boosting the green content (at the expense of other wavelengths) increases the output in lumens, but does not necessarily make for a better light source.
spidermother, Jul 20 2012


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